A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In lithographic apparatus, various optical elements are provided, especially very thin and fragile optical elements. These elements should be positioned accurately and in a fixed position.
Presently known methods for positioning optical elements include frames in which the elements may be contained. The frames are often provided with connecting elements for fixture to, for example, a frame of the apparatus. Such frames often need a relatively large amount of material and volume for positioning and fixture.
Furthermore, it is known to use adhesives for fixing optical elements in an apparatus. This is undesirable because of potential contamination of the optical element and its surroundings. Chemical elements may be released from the adhesive, especially when it is excited by radiation, for example, a light beam, during use of the apparatus.